粘土科学

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Clay-humus complex has an important role for humic substances are stable in soil. There are many researches about clay-humus complex of volcanic ash soils, but few researches about that of red-yellow soils. In this paper we presented that characteristics for clay-humus complex of red-yellow soils in Okinawa beech forest. Sampling sites were 4 sites, 3 soil samples (3 horizons) were collected in each sites. Clay, silt and sand fractions were in the range of 312〜505 g kg^<-1>, 314〜389 g kg^<-1> and 128〜351 g kg^<-1>, respectively. From X-ray analysis, clay minerals were kaolin minerals, mica and vermiculite-chlorite integrate. Three kinds of humic substance (HS) were extracted and quantified. Two kinds of humic substance were extracted by NaOH and Na_4P_2O_7, humin were not able to extract by both chemical regents. Humin content was higher than other HS fractions. Generally, humin is stable fraction in soil, but other kinds of HS are not stable. Some cations are necessary to stabilize the unstable HS indicated that extractable fraction by regent in soil. Al and Fe content in HS fractions extracted by NaOH and Na_4P_2O_7 were higher than other cations. There were significant relationship between carbon content extracted by NaOH and Ca and Fe with NaOH, and carbon content extracted by Na_4P_2O_7 and Ca and Al with Na_4P_2O_7. These data indicated that HS extracted by both NaOH and Na_4P_2O_7 were stable by these cations. Especially, adding the effects of Fe and Al, calcium may affect the stabilization of both HS types. It is suggested that Fe and Al, Ca are essential to form clay-humus complex in red-yellow soil.

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H^+-form geopolymer powder was prepared by grinding a Na^+-form geopolymer hardened paste and processing it with sulfuric acid. At pH 7, the extent of cation exchange with Na^+ and K^+ ions of the H^+-form geopolymer powder was one-fourth of that of the original Na^+-form geopolymer at the same pH. The ion-exchange capacity of the H^+-form geopolymer powder showed pH dependence, that is, a tendency to increase with increasing pH. Additionally, we observed that the H^+-form geopolymer powder adsorbed Na^+ ions from and lowered the pH of the hardened cement paste. However, in solution at pH 12.5, a part of the Si component of the H^+-form geopolymer powder was leached out. It was thus confirmed that other alkaline-adsorption mechanisms, by which the leached Si-component reacts with the alkaline component of the cement paste, are at work, and therefore, they need to be considered in addition to the cation-exchange reaction in order to understand completely the behavior of the H^+-form geopolymer in cement paste.

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